1. Field of the Invention
The present invention relates to an information recording and reproducing method, an information recording and reproducing system, an information recording apparatus, and an information reproducing apparatus, and more particularly relates to an information recording and reproducing method, an information recording and reproducing system, an information recording apparatus and an information reproducing apparatus, which can record and reproduce digital data onto and from an information recording medium.
2. Description of the Related Art
There is a research with regard to a technique for recording or reproducing multi-level digital data having a plurality of values other than xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d onto or from an information recording medium in order to record or reproduce a large amount of digital data onto or from an optical disc as the information recording medium, at a high density.
Here, as a conventional technique in this field, there is a recording and reproducing method, which is a combination of (i) a pit edge multi-level recording method for changing the edge positions of a pit formed on the optical disc (namely, the positions of two edges of the pit in a rotational direction of the optical disc), by several steps in the rotational direction depending upon a value of digital data to be recorded to thereby record the digital data, and (ii) an RPR (Radial direction Partial Response) reproducing method for reproducing the recorded digital data by simultaneously reading the edges of pits on two tracks adjacent to each other. Such a recording and reproducing method is disclosed in detail in, for example, Japanese Patent Application Laid Open publication NO. Hei 10-74322.
Next, the above-mentioned information recording and reproducing method is schematically explained below with reference to FIG. 10 to FIG. 12C. FIG. 10 is a block diagram showing the schematic configuration of an information recording and reproducing system used in the information recording and reproducing method. FIG. 11 is an enlarged plan view showing an aspect of the pit on the optical disc. FIG. 12A to FIG. 12C are timing charts describing the information recording and reproducing method.
As shown in FIG. 10, a conventional information recording and reproducing system Sxe2x80x2 is provided with a recording system Rxe2x80x2 for digitally recording information data Sin onto an optical disc 1 and a reproducing system Pxe2x80x2 for reproducing the recorded information data Sin from the optical disc 1 to thereby generate reproduction data Sout.
Next, the detailed configuration and operation of the recording system Rxe2x80x2 is explained below.
As shown in FIG. 10, the recording system Rxe2x80x2 is provided with a Reed Solomon encoding unit 100, a mapping unit 101, a pre-coding unit 102, a pit edge modulating unit 103 and a recording head 104.
Next, the operations of the respective units are explained below.
The Reed Solomon encoding unit 100 performs an encoding process including an addition of a Reed Solomon error correction code onto the information data Sin, and generates an information code Se, and then outputs it to the mapping unit 101.
Accordingly, the mapping unit 101 converts the information code Se corresponding to a plurality of bits among the inputted information code Se, into a multi-level symbol Sts, and outputs it to the pre-coding unit 102. Actually, for example, the information code Se corresponding to three bits is converted into two of the multi-level symbols Sts having three levels of xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d and xe2x80x9c2xe2x80x9d.
Next, the pre-coding unit 102 performs a pre-coding operation onto the generated multi-level symbol Sts, and converts the multi-level symbol Sts into a record symbol Srs similarly having the three levels of xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d and xe2x80x9c2xe2x80x9d, and then outputs it to the pit edge modulating unit 103.
Then, the pit edge modulating unit 103 generates a record pulse Srp, whose edge positions (namely, a rising up position and a falling down position of the pulse) are changed by three steps in accordance with respective values in the generated record symbols Srs, and then outputs it to the recording head 104.
Accordingly, the recording head 104 irradiates a record laser light, whose intensity is modulated in accordance with the record pulse Srp, onto a track (not shown) of the optical disc 1, and forms on the track a pit row composed of pits having edges (implying two edges existing in a rotational direction of the optical disc 1, and hereafter, implying the same) at positions corresponding to the generated record pulse Srp.
The above-mentioned operations of the recording system Rxe2x80x2 enables the original information data Sin to be recorded on the optical disc 1, by using the pits in which the edge position is changed by the three steps.
The detailed configuration and operation of the reproducing system Pxe2x80x2 is explained below.
As shown in FIG. 10, the reproducing system Pxe2x80x2 is provided with a reproducing head 105, a waveform equalizer 106, a level judging unit 107, a remainder calculating unit 108, a reverse mapping unit 109 and a Reed Solomon decoding unit 110.
The operations of the respective units are explained below.
The reproducing head 105 irradiates a reproduction laser light having a constant intensity onto the optical disc 1, reads the formed pit row, generates an analog reproduction signal Spa having a level corresponding to the edge position of the pit, and outputs it to the waveform equalizer 106.
A beam spot formed on the optical disc 1 by the reproduction laser light is moved on a central line between two tracks adjacent to each other, and two pit edges on the two tracks adjacent to each other are read at the same time. Thus, a level of the generated analog reproduction signal Spa corresponds to an added value of the two record symbols Srs recorded on the two tracks adjacent to each other. In a case of the above-mentioned record symbol Srs having the three levels of xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d and xe2x80x9c2xe2x80x9d, the reproduction analog signal Spa takes five levels composed of xe2x80x9c0xe2x80x9d (if the values of the two record symbols Srs adjacent to each other are both xe2x80x9c0xe2x80x9d), xe2x80x9c1xe2x80x9d (if the values of the two record symbols Srs are xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d), xe2x80x9c2xe2x80x9d (if the values of the two record symbols Srs are xe2x80x9c0xe2x80x9d and xe2x80x9c2xe2x80x9d, or both xe2x80x9c1xe2x80x9d), xe2x80x9c3xe2x80x9d (if the values of the two record symbols Srs are xe2x80x9c1xe2x80x9d and xe2x80x9c2xe2x80x9d), or xe2x80x9c4xe2x80x9d (if the values of the two record symbols Srs are both xe2x80x9c2xe2x80x9d).
Next, the waveform equalizer 106 filters the generated reproduction analog signal Spa by using a filter having a frequency characteristic of a high frequency band emphasis type, and re-shapes its waveform, to thereby generate a re-shaped analog reproduction signal Sep. Then, the waveform equalizer 106 outputs it to the level judging unit 107.
Accordingly, the level judging unit 107 samples the re-shaped analog reproduction signal Sep by using a preset sampling clock, and compares its voltage level with four threshold levels, and then generates a judgment symbol Sjs of five levels corresponding to the reproduction analog signal Spa of the five levels, and further outputs it to the remainder calculating unit 108.
Next, the remainder calculating unit 108 calculates the respective remainders when the respective values (xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c2xe2x80x9d, xe2x80x9c3xe2x80x9d and xe2x80x9c4xe2x80x9d) of the generated judgment symbol Sjs are divided by 3, and generates a reproduction symbol Sps having three levels of xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d and xe2x80x9c2xe2x80x9d, and then outputs it to the reverse mapping unit 109.
Then, the reverse mapping unit 109 carries out a converting process inverse to that of the mapping unit 101, and converts the two reproduction symbols Sps into a reproduction information code Spe of three bits, and then outputs it to the Reed Solomon decoding unit 110.
Finally, the Reed Solomon decoding unit 110 performs a demodulating process using the Reed Solomon error correction code onto the reproduction information code Spe, and generates the final reproduction data Sout, and then outputs it to the external portion.
In the above-mentioned information recording and reproducing system Sxe2x80x2, the pre-coding operation is done in the recording system Rxe2x80x2, and on the contrary, the addition of the two record symbols Srs and the remainder calculation are done in the reproducing system Pxe2x80x2. Here, the pre-coding operation in the recording system Rxe2x80x2 and the addition/remainder calculation in the reproducing system Pxe2x80x2 have the relationship of the calculation inverse to each other. Thus, the original information data Sin can be recovered as the reproduction data Sout, through the recording system Rxe2x80x2 and the reproducing system Pxe2x80x2.
Next, the shape of the pit in the optical disc 1 is explained below with reference to FIG. 11.
As shown in FIG. 11, in the pit edge multi-level recording method, the pit row having a constant cycle is formed with pits PT on a track TR. Also, the position of the pit edge in each pit PT is changed by the three steps in the rotational direction of the optical disc 1, in accordance with the value of the record symbol Srs of the above-mentioned three levels. In addition, in FIG. 11, the positions that can be considered as the position of the pit edge in each pit PT are all shown by using solid lines. Actually, the pit edge is formed at any one position of the three pit edge positions.
On the other hand, the reproduction laser light irradiated onto the optical disc 1 at the time of the reproduction generates a beam spot BS having an irradiation range represented by a circle in FIG. 11. Then, the movement of the beam spot BS on a central line L between two tracks TR represented by a dashed line enables the record symbols Srs recorded in the two pit edges on the two tracks TR to be read at the same time.
Next, an operational waveform in the information recording and reproducing system Sxe2x80x2 is explained below with reference to FIG. 12A, FIG. 12B and FIG. 12C. FIG. 12A is a timing chart showing an example of a waveform of the record pulse Srp. FIG. 12B is an enlarged plan view showing a shape of a corresponding pit PT on the optical disc 1, and FIG. 12C is a timing chart showing an example of a waveform of a corresponding analog reproduction signal Spa.
Here, FIG. 12A shows three kinds of rising up timings and falling down timings that can be considered as the record pulse Srp, under a condition that all of them overlap with each other. However, the record pulse Srp in the actual recording system Rxe2x80x2 has just one rising up timing and just one falling down timing of the three rising up timings and falling down timings shown in FIG. 12A.
In FIG. 12B, similarly to the case of FIG. 11, the actual pit PT has a pit edge at only one position of the three pit edge positions.
Moreover, FIG. 12C shows many waveforms that can be detected as the analog reproduction signal Spa, under the condition that all of them overlap with each other. However, the analog reproduction signal Spa in the actual reproducing system Pxe2x80x2 has just one waveform of the many waveforms shown in FIG. 12C. Furthermore, FIG. 12C shows a case that a level of the analog reproduction signal Spa becomes higher when the pit PT is read.
As shown in FIG. 12A, the record pulse Srp is generated which has a constant cycle 2T. A central value of a length of the pulse is xe2x80x9cTxe2x80x9d (this implies a length of a time period while the record pulse Srp is at a xe2x80x9cHIGHxe2x80x9d level, and hereafter, also implies the same).
Also, the rising up timing and the falling down timing of the record pulse Srp are respectively changed by the three steps, under a step width of a time period 3t, in accordance with a content of the record symbol Srs. Actually, if the value of the record symbol Srs is xe2x80x9c0xe2x80x9d, the rising up timing or the falling down timing is shifted by the time period 3t, in a direction in which the pulse length in the record pulse Srp is made shorter. On the other hand, if the value of the record symbol Srs is xe2x80x9c1xe2x80x9d, the rising up timing or the falling down timing is set at respective central values. Moreover, if the value of the record symbol Srs is xe2x80x9c2xe2x80x9d, the rising up timing or the falling down timing is similarly shifted by the time period 3t, in a direction in which the pulse length is made longer.
As a result, the pulse length of the record pulse Srp can take five values of xe2x80x9cTxe2x88x926txe2x80x9d, xe2x80x9cTxe2x88x923txe2x80x9d, xe2x80x9cTxe2x80x9d, xe2x80x9cT+3txe2x80x9d and xe2x80x9cT+6txe2x80x9d.
In accordance with the record pulse Srp having such a waveform, the pit PT on the optical disc 1 is formed to have the constant cycle 2D, as shown in FIG. 12B, and a central value of each pit length is xe2x80x9cDxe2x80x9d.
Moreover, the position of the edge of each pit PT is changed by the three steps under a step width of each distance 3d, in accordance with the waveform of the record pulse Srp.
As a result, the pit length of the pit PT can take five values of xe2x80x9cDxe2x88x926dxe2x80x9d, xe2x80x9cDxe2x88x923dxe2x80x9d, xe2x80x9cDxe2x80x9d, xe2x80x9cD+3dxe2x80x9d and xe2x80x9cD+6dxe2x80x9d.
Next, at the time of the reproduction, the voltage level of the analog reproduction signal Spa is sampled, for example, at the sampling points indicated at the times t1, t2, t3 and t4 shown in FIG. 12C.
At this time, the voltage level is changed by five steps under a step width of a voltage 3e with a central value as xe2x80x9cExe2x80x9d, in accordance with the positions of the respective edges in the two pits PT read by the reproducing head 105 at the same time. As a result, when the sum of the two record symbols Srs corresponding to the two edges read at the same time is xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c2xe2x80x9d, xe2x80x9c3xe2x80x9d or xe2x80x9c4xe2x80x9d, respectively, the voltage level of the analog reproduction signal Spa is xe2x80x9cExe2x88x926exe2x80x9d, xe2x80x9cExe2x88x923exe2x80x9d, xe2x80x9cExe2x80x9d, xe2x80x9cE+3exe2x80x9d or xe2x80x9cE+6exe2x80x9d, respectively. Then, those voltage levels are compared with the four threshold levels having the values xe2x80x9cExe2x88x924. 5exe2x80x9d, xe2x80x9cExe2x88x921. 5exe2x80x9d, xe2x80x9cE+1. 5exe2x80x9d and xe2x80x9cE+4. 5exe2x80x9d, respectively. Then, the above-mentioned judgment symbol Sjs can be determined if the level judgment is done by the level judging unit 107.
Then, the reproduction symbol Sps can be recovered as the remainder calculating unit 108 performs the remainder calculation onto the judgment symbol Sjs.
As mentioned above, the pit edge multi-level recording method records the record symbol Srs onto the optical disc 1 as the change of the position of the pit edge, and then judges the voltage level of the analog reproduction signal Spa obtained by the reproduction from the optical disc 1. Accordingly, the multi-level symbol Sts can be recovered as the reproduction symbol Sps.
However, in the above mentioned information recording and reproducing system Sxe2x80x2, if it is assumed to record the record symbols Srs of two values in one pit edge, and to read only one pit edge at one time, the voltage levels of the analog reproduction signals Spa representing one record symbols Srs are separated by xe2x80x9c12exe2x80x9d from each other.
On the contrary, if the record symbols Srs of the three values are recorded in one pit edge and two pit edges are read at one time, as mentioned above, the voltage levels of the analog reproduction signals Spa representing two record symbols Srs are separated only by xe2x80x9c3exe2x80x9d from each other.
In this case, the level of the analog reproduction signal Spa is subdivided by recording the multi-level record symbol Srs and by detecting the plurality of pit edges at one time. This subdivision reduces the S/N ratio of the analog reproduction signal Spa when its voltage level is judged.
In the reproduction process, the SIN ratio may be further reduced by various disturbances such as a disc noise included in the optical disc 1, or a laser noise included in the reproduction laser light, or a circuit noise, or servo errors (a focus error or a tracking error of the reproducing head 105), or disc tilt (i.e., a deviation from a right angle of the angle between an optical axis of the reproduction laser light and an information recording surface of the optical disc 1). If the S/N ratio is further reduced, or if the waveform of the analog reproduction signal Spa is distorted by these disturbances, it is further difficult to judge the voltage level of the analog reproduction signal Spa accurately.
As mentioned above, if the multi-level digital data is recorded onto or reproduced from the optical disc 1, the various disturbances cause the error rate of the reproduction data Sout to be easily deteriorated, which results in a problem of a reduction in a reliability as the information recording and reproducing system Sxe2x80x2.
The present invention is proposed in view of the above mentioned problems. It is therefore an object of the present invention to provide an information recording and reproducing method, an information recording and reproducing system, an information recording apparatus and an information reproducing apparatus, which can avoid a deterioration of an error rate in reproduction data, even if multi-level digital data is optically recorded onto or reproduced from an information recording medium and there is a possibility that various disturbances may be applied onto it, and which can improve a reliability of the system or apparatus.
The above object of the present invention can be achieved by an information recording and reproducing method provided with an information recording method of optically recording digital data onto an information recording medium such as an optical disc etc., by forming a pit having a shape corresponding to the digital data, and an information reproducing method of optically reproducing the recorded digital data from the information recording medium. The information recording method is provided with: a record code generating process of applying an encoding process using a convolutional code onto the digital data, to thereby convert the digital data into a record code; a multi-level symbol generating process of converting the generated record code corresponding to a plurality of bits into a multi-level symbol having a plurality of values; a record symbol generating process of applying a logical converting process onto the generated multi-level symbol to thereby convert the multi-level symbol into a record symbol; and a recording process of recording the record symbol onto the information recording medium by optically forming the pit on the information recording medium while changing the shape of the pit by several steps in correspondence with a value of the generated record symbol. The information reproducing method is provided with: an irradiating process of irradiating a light beam for reproducing the digital data so that an irradiation range of the light beam on the information recording medium of the light beam covers a plurality of pits; a detecting process of detecting the record symbol as an analog detection signal, on the basis of a reflection light of the light beam from the irradiation range; an analog-to-digital converting process of converting the analog detection signal into a sample value series, which is a digital signal; and a recovering process of applying a Viterbi decoding process onto the converted sample value series to thereby recover the digital data.
According to the information recording and reproducing method of the present invention, at the time of recording the information, the record symbol, which is generated by the encoding processing using the convolutional code, is recorded onto the information recording medium as the shape of the pit is changed by the several steps. At the time of reproducing the information, the light beam is irradiated so that a plurality of pits are within the irradiation range, and the original digital data is reproduced by the Viterbi decoding process on the basis of the reflection light of the irradiated light beam. Thus, even if there are various external disturbances in case that the digital data is recorded as the shape of the pit is changed by the several steps, it is possible to reduce the error rate and reproduce the digital data.
Therefore, since the error rate at the time of reproducing the information can be reduced even in the information recording and reproducing system which is subjected to the various external disturbance, it is possible to improve the reliability of the information recording and reproducing system.
In one aspect of the information recording and reproducing method of the present invention, the record symbol generating process is provided with a pre-coding process of applying a pre-coding operation, which is set in advance in correspondence with the detecting process, onto (i) the multi-level symbol corresponding to one pit of the plurality of pits, which are within the irradiation range in the irradiating process, and (ii) the record symbol corresponding to another pit of the plurality of pits, which are within the irradiation range in the irradiating process, to thereby generate the record symbol corresponding to the one pit.
According to this aspect, the pre-coding process corresponding to the detecting process is applied onto the multi-level symbol corresponding to one pit of the plurality of pits within the irradiation range and the record symbol corresponding to another pit of the plurality of pits within the irradiation range, so that the record symbol corresponding to the one pit is generated. Thus, at the time of reproducing the information, it is possible to correctly recover the digital data, which is recorded in one pit, from the reflection light of a plurality of pits.
In another aspect of the information recording and reproducing method of the present invention, the convolutional code is a punctured code.
According to this aspect, it is possible to record the digital data with generating the record code at a high encoding rate.
In another aspect of the information recording and reproducing method of the present invention, in the multi-level symbol generating process, a converting process based on a Gray code is used to generate the multi-level symbol.
According to this aspect, it is possible to improve the reproduction capability at the time of reproducing the information.
In another aspect of the information recording and reproducing method of the present invention, a branch metric calculating process in the Viterbi decoding process compares values of a plurality of branch metrics with each other, and selects one branch metric having a minimum value.
According to this aspect, one branch metric having the minimum value is selected among a plurality of branch metrics in the Viterbi decoding process, and the pass metric is calculated by using the selected small number of branch metrics. Thus, it is possible to miniaturize a circuit for performing the Viterbi decoding process.
In another aspect of the information recording and reproducing method of the present invention, in the recording process, the pit is formed by changing an edge position of the pit by several steps in accordance with the value of the generated record symbol, and in the irradiating process, the light beam is irradiated such that a plurality of edge positions of the pits are within the irradiation range.
According to this aspect, since the position of the pit edge is the edge position corresponding to the multi-level record symbol, it is possible to accurately and easily reproduce the analog reproduction signal corresponding to the sum of the record symbol recorded on the plurality of pits, and it is further possible to more accurately reproduce the digital data.
The above object of the present invention can be achieved by an information recording and reproducing system provided with an information recording apparatus for optically recording digital data onto an information recording medium such as an optical disc etc., by forming a pit having a shape corresponding to the digital data, and an information reproducing apparatus for optically reproducing the recorded digital data from the information recording medium. The information recording apparatus is provided with: a record code generating device such as a convolutional encoding unit etc., for applying an encoding process using a convolutional code onto the digital data, to thereby convert the digital data into a record code; a multi-level symbol generating device such as a mapping unit etc., for converting the generated record code corresponding to a plurality of bits into a multi-level symbol having a plurality of values; a record symbol generating device such as a pre-coding unit etc., for applying a logical converting process onto the generated multi-level symbol to thereby convert the multi-level symbol into a record symbol; and a recording device such as a recording head etc., for recording the record symbol onto the information recording medium by optically forming the pit on the information recording medium while changing the shape of the pit by several steps in correspondence with a value of the generated record symbol. The information reproducing apparatus is provided with: an irradiating device such as a reproducing head etc., for irradiating a light beam for reproducing the digital data so that an irradiation range of the light beam on the information recording medium covers a plurality of pits; a detecting device such as a reproducing head etc., for detecting the record symbol as an analog detection signal, on the basis of a reflection light of the light beam from the irradiation range; an analog-to-digital converting device such as an A/D convertor etc., for converting the analog detection signal into a sample value series, which is a digital signal; and a recovering device such as a Viterbi decoding unit etc., for applying a Viterbi decoding process onto the converted sample value series to thereby recover the digital data.
According to the information recording and reproducing system of the present invention, at the time of recording the information, the record symbol, which is generated by the encoding processing using the convolutional code, is recorded onto the information recording medium as the shape of the pit is changed by the several steps. At the time of reproducing the information, the light beam is irradiated so that a plurality of pits are within the irradiation range, and the original digital data is reproduced by the Viterbi decoding process on the basis of the reflection light of the irradiated light beam. Thus, even if there are various external disturbances in case that the digital data is recorded as the shape of the pit is changed by the several steps, it is possible to reduce the error rate and reproduce the digital data.
Therefore, since the error rate at the time of reproducing the information can be reduced even in the information recording and reproducing system which is subjected to the various external disturbance, it is possible to improve the reliability of the information recording and reproducing system.
The above object of the present invention can be also achieved by an information recording apparatus for optically recording digital data onto an information recording medium such as an optical disc etc., by forming a pit having a shape corresponding to the digital data, which is optically reproduced from the information recording medium by irradiating a light beam for reproducing the digital data so that an irradiation range of the light beam on the information recording medium covers a plurality of pits and by applying a Viterbi decoding process onto an analog signal detected on the basis of a reflection light of the light beam from the irradiation range. The information recording apparatus is provided with: a record code generating device such as a convolutional encoding unit etc., for applying an encoding process using a convolutional code onto the digital data, to thereby convert the digital data into a record code; a multi-level symbol generating device such as a mapping unit etc., for converting the generated record code corresponding to a plurality of bits into a multi-level symbol having a plurality of values; a record symbol generating device such as a pre-coding unit etc., for applying a logical converting process onto the generated multi-level symbol to thereby convert the multi-level symbol into a record symbol; and a recording device such as a recording head etc., for recording the record symbol onto the information recording medium by optically forming the pit on the information recording medium while changing the shape of the pit by several steps in correspondence with a value of the generated record symbol.
According to the information recording apparatus of the present invention, at the time of recording the information, the record symbol, which is generated by the encoding processing using the convolutional code, is recorded onto the information recording medium as the shape of the pit is changed by the several steps. At the time of reproducing the information, the light beam is irradiated so that a plurality of pits are within the irradiation range, and the original digital data is reproduced by the Viterbi decoding process on the basis of the reflection light of the irradiated light beam. Thus, even if there are various external disturbances in case that the digital data is recorded as the shape of the pit is changed by the several steps, it is possible to reduce the error rate and reproduce the digital data.
Therefore, since the error rate at the time of reproducing the information can be reduced even in the information recording and reproducing system which is subjected to the various external disturbance, it is possible to improve the reliability of the information recording and reproducing system.
In one aspect of the information recording apparatus of the present invention, the record symbol generating device is provided with a pre-coding device for applying a pre-coding operation, which is set in advance in correspondence with a reproducing process for the digital data, onto (i) the multi-level symbol corresponding to one pit of the plurality of pits, which are within the irradiation range in the reproducing process, and (ii) the record symbol corresponding to another pit of the plurality of pits, which are within the irradiation range in the reproducing process, to thereby generate the record symbol corresponding to the one pit.
According to this aspect, the pre-coding process corresponding to the reproducing process for the digital data is applied onto the multi-level symbol corresponding to one pit of the plurality of pits within the irradiation range and the record symbol corresponding to another pit of the plurality of pits within the irradiation range, so that the record symbol corresponding to the one pit is generated. Thus, at the time of reproducing the information, it is possible to correctly recover the digital data, which is recorded in one pit, from the reflection light of a plurality of pits.
In another aspect of the information recording apparatus of the present invention, the convolutional code is a punctured code.
According to this aspect, it is possible to record the digital data with generating the record code at a high encoding rate.
In another aspect of the information recording apparatus of the present invention, in the multi-level symbol generating device, a converting process based on a Gray code is used to generate the multi-level symbol.
According to this aspect, it is possible to improve the reproduction capability at the time of reproducing the information.
In another aspect of the information recording apparatus of the present invention, by the recording device, the pit is formed by changing an edge position of the pit by several steps in accordance with the value of the generated record symbol, and in a reproducing process for the digital data, the light beam is irradiated such that a plurality of edge positions of the pits are within the irradiation range.
According to this aspect, since the position of the pit edge is the edge position corresponding to the multi-level record symbol, it is possible to accurately and easily reproduce the analog reproduction signal corresponding to the sum of the record symbol recorded on the plurality of pits, and it is further possible to more accurately reproduce the digital data.
The above object of the present invention can be also achieved by an information reproducing apparatus for optically reproducing digital data from an information recording medium such as an optical disc etc., on which the digital data is recorded by (i) applying an encoding process using a convolutional code onto the digital data, to thereby convert the digital data into a record code, (ii) converting the generated record code corresponding to a plurality of bits into a multi-level symbol having a plurality of values, (iii) applying a logical converting process onto the generated multi-level symbol to thereby convert the multi-level symbol into a record symbol, and (iv) recording the record symbol onto the information recording medium by optically forming a pit having a shape corresponding to the digital data on the information recording medium while changing the shape of the pit by several steps in correspondence with a value of the generated record symbol. The information reproducing apparatus is provided with: an irradiating device such as a reproducing head etc., for irradiating a light beam for reproducing the digital data so that an irradiation range of the light beam on the information recording medium covers a plurality of pits; a detecting device such as a reproducing head etc., for detecting the record symbol as an analog detection signal, on the basis of a reflection light of the light beam from the irradiation range; an analog-to-digital converting device such as an A/D convertor etc., for converting the analog detection signal into a sample value series, which is a digital signal; and a recovering device such as a Viterbi decoding unit etc., for applying a Viterbi decoding process onto the converted sample value series to thereby recover the digital data.
According to the information reproducing apparatus of the present invention, the digital data is recorded on the information recording medium by changing the shape of the pit by several steps in correspondence with the record symbol, which is generated by the encoding processing using the convolutional code. At the time of reproducing the information, the light beam is irradiated so that a plurality of pits are within the irradiation range, and the original digital data is reproduced by the Viterbi decoding process on the basis of the reflection light of the irradiated light beam. Thus, even if there are various external disturbances in case that the digital data is recorded as the shape of the pit is changed by the several steps, it is possible to reduce the error rate and reproduce the digital data.
Therefore, since the error rate at the time of reproducing the information can be reduced even in the information recording and reproducing system which is subjected to the various external disturbance, it is possible to improve the reliability of the information recording and reproducing system.
In one aspect of the information reproducing apparatus of the present invention, a branch metric calculating process in the Viterbi decoding process compares values of a plurality of branch metrics with each other, and selects one branch metric having a minimum value.
According to this aspect, one branch metric having the minimum value is selected among a plurality of branch metrics in the Viterbi decoding process, and the pass metric is calculated by using the selected small number of branch metrics. Thus, it is possible to miniaturize a circuit for performing the Viterbi decoding process.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read conjunction with the accompanying drawings briefly described below.